The invention is related to the monitoring of vehicular components, systems and subsystems as well as to the measurement of physical and chemical characteristics relating to the vehicle or its components, systems and subsystems and using the measurements to control and/or affect one or more vehicular systems. Some of the systems which are monitored can include the tires. As generally used herein, a tire is made of a rubber substrate defining side walls and a tread. The tire is mounted on a wheel rim so that a wheel as generally used herein, includes a tire and a wheel rim.
Tire monitoring is now extremely important since NHTSA (National Highway Traffic Safety Administration) has recently linked 148 deaths and more than 525 injuries in the United States to separations, blowouts and other tread problems in Firestone's ATX, ATX II and Wilderness AT tires, 5 million of which were recalled in 2000. Many of the tires were standard equipment on the Ford Explorer. Ford recommends that the Firestone tires on the Explorer sport utility vehicle be inflated to 26 psi, while Firestone recommends 30 psi. It is surprising that a tire can go from a safe condition to an unsafe condition based on an under inflation of 4 psi as suggested by Firestone.
According to a NHTSA research survey, 27% of passenger cars on U.S. roadways are driven with one or more substantially under-inflated tires. In addition, the survey found that 33% of light trucks (including sport utility vehicles, vans and pickup trucks) are driven with one or more substantially under-inflated tires.
Recent studies in the United States conducted by the Society of Automotive Engineers show that low tire pressure causes about 260,000 accidents annually. Another finding is that about 75% of tire failures each year are preceded by slow air leaks or inadequate tire inflation. Nissan, for example, warns that incorrect tire pressures can compromise the stability and overall handling of a vehicle and can contribute to an accident. Additionally, most non-crash auto fatalities occur while drivers are changing flat tires. Thus, tire failures are clearly a serious automobile safety problem that requires a solution.
About 16% of all car accidents are a result of incorrect tire pressure. Thus, effective pressure and wear monitoring is extremely important. Motor Trend magazine stated that one of the most overlooked maintenance areas on a car is tire pressure. An estimated 40% to 80% of all vehicles on the road are operating with under-inflated tires. When under-inflated, a tire tends to flex its sidewall more, increasing its rolling resistance which decreases fuel economy. The extra flex also can create excessive heat in the tire that can shorten its service life.
The Society of Automotive Engineers reports that about 87% of all flat tires have a history of under-inflation. About 85% of pressure loss incidents are slow punctures caused either by small-diameter objects trapped in the tire or by larger diameter nails. The leak will be minor as long as the nail is trapped. If the nail comes out, pressure can decrease rapidly. Incidents of sudden pressure loss are potentially the most dangerous for drivers and account for about 15% of all cases.
A properly inflated tire loses approximately 1 psi per month. A defective or worn tire can lose pressure at a more rapid rate. About 35% of the recalled Bridgestone tires had improper repairs.
Research from a variety of sources suggests that under-inflation can be significant to both fuel economy and tire life. Industry experts have determined that tires under-inflated by a mere 10% wear out about 15% faster. An average driver with an average set of tires can drive an extra 5,000 to 7,000 miles before buying new tires by keeping the tire properly inflated.
The American Automobile Association has determined that under-inflated tires cut a vehicle's fuel economy by as much as 2% per psi below the recommended level. If each of a car's tires is supposed to have a pressure of 30 psi and instead has a pressure of 25 psi, the car's fuel efficiency drops by about 10%. Depending on the vehicle and miles driven, that could cost the owner from $100 to $500 a year.
The ability to control a vehicle is strongly influenced by tire pressure. When the tire pressure is kept at proper levels, optimum vehicle braking, steering, handling and stability are accomplished. Low tire pressure can also lead to damage to both the tires and wheels.
A Michelin study revealed that the average driver does not recognize a low tire until it is 14 psi too low. One of the reasons is that today's radial tire is hard to judge visually because the sidewall flexes even when properly inflated.
Despite all the recent press about keeping tires properly inflated, new research shows that most drivers do not know the correct inflation pressure. In a recent survey, only 45% of respondents knew where to look to find the correct pressure, even though 78% thought they knew. Twenty-seven percent incorrectly believed the sidewall of the tire carries the correct information and did not know that the sidewall only indicates the maximum pressure for the tire, not the optimum pressure for the vehicle. In another survey, about 60% of the respondents reported that they check tire pressure but only before going on a long trip. The National Highway Traffic Safety Administration estimates that at least one out of every five tires is not properly inflated.
The problem is exacerbated with the new run-flat tires where a driver may not be aware that a tire is flat until it is destroyed. Run-flat tires can be operated at air pressures below normal for a limited distance and at a restricted speed (e.g., 125 miles at a maximum of 55 mph). The driver must therefore be warned of changes in the condition of the tires so that she can adapt her driving to the changed conditions.
One solution to this problem is to continuously monitor the pressure and perhaps the temperature in the tire. Pressure loss can be automatically detected in two ways: by directly measuring air pressure within the tire or by indirect tire rotation methods. Various indirect methods are based on the number of revolutions each tire makes over an extended period of time through the ABS system and others are based on monitoring the frequency changes in the sound emitted by the tire. In the direct detection case, a sensor is mounted into each wheel or tire assembly, each with its own identity. An on-board computer collects the signals, processes and displays the data and triggers a warning signal in the case of pressure loss.
Under-inflation is not the only cause of sudden tire failure. A variety of mechanical problems including a bad wheel bearing or a “dragging” brake can cause the tire to heat up and fail. In addition, as may have been a contributing factor in the Firestone case, substandard materials can lead to intra-tire friction and a buildup of heat. The use of re-capped or over-loaded truck tires is another example of heat caused failure as a result of intra-tire friction. An overheated tire can fail suddenly without warning.
As discussed in more detail below, direct tire monitors permit the driver to check the vehicle tire pressures from inside the vehicle.
The Transportation Recall Enhancement, Accountability and Documentation Act, (H.R. 5164, or Public Law No. 106-414) known as the TREAD Act, was signed by President Clinton on Nov. 1, 2000. Section 12, TIRE PRESSURE WARNING, states that: “Not later than one year after the date of enactment of this Act, the Secretary of Transportation, acting through the National Highway Traffic Safety Administration, shall complete a rulemaking for a regulation to require a warning system in a motor vehicle to indicate to the operator when a tire is significantly under-inflated. Such requirement shall become effective not later than 2 years after the date of the completion of such rulemaking.” Thus, it is expected that a rule requiring continuous tire monitoring will take effect for the 2004 model year.
This law will dominate the first generation of such systems as automobile manufacturers move to satisfy the requirement. In subsequent years, more sophisticated systems will be developed that in addition to pressure, will monitor temperature, tire footprint, wear, vibration, etc. Although TREAD requires that the tire pressure be monitored, it is believed by the inventors that other parameters are as important as the tire pressure or even more important than the tire pressure as described in more detail below.
Consumers are also in favor of tire monitors. Johnson Controls' market research showed that about 80% of consumers believe a low tire pressure warning system is an important or extremely important vehicle feature. Thus, as with other safety products such as airbags, competition to meet customer demands will soon drive this market.
Although, as with most other safety products, the initial introductions will be in the United States, speed limits in the United States and Canada are sufficiently low that tire pressure is not as critical an issue as in Europe, for example, where the drivers often drive much faster.
The advent of microelectromechanical (MEMS) pressure sensors, especially those based on surface acoustical wave (SAW) technology, has now made the wireless and powerless monitoring of tire pressure feasible. This is the basis of some of the tire pressure monitors described below. According to a Frost and Sullivan report on the U.S. Micromechanical Systems (MEMS) market (June 1997): “A MEMS tire pressure sensor represents one of the most profound opportunities for MEMS in the automotive sector.”
There are many wireless tire temperature and pressure monitoring systems disclosed in the prior art patents such as for example, U.S. Pat. Nos. 4,295,102, 4,296,347, 4,317,372, 4,534,223, 5,289,160, 5,612,671, 5,661,651, 5,853,020 and 5,987,980 and International Publication No. WO 01/07271(A1), all of which are illustrative of the state of the art of tire monitoring and are incorporated by reference herein.
Devices for measuring the pressure and/or temperature within a vehicle tire directly can be categorized as those containing electronic circuits and a power supply within the tire, those which contain electronic circuits and derive the power to operate these circuits either inductively, from a generator or through radio frequency radiation, and those that do not contain electronic circuits and receive their operating power only from received radio frequency radiation. For the reasons discussed above, the discussion herein is mainly concerned with the latter category. This category contains devices that operate on the principles of surface acoustic waves (SAW) and the disclosure below is concerned primarily with such SAW devices although in some cases RFID devices are also used.
International Publication No. WO 01/07271 describes a tire pressure sensor that replaces the valve and valve stem in a tire.
U.S. Pat. No. 5,231,827 contains a basic description and background of the tire-monitoring problem. The device disclosed, however, contains a battery and electronics and is not a SAW device. Similarly, the device described in U.S. Pat. No. 5,285,189 contains a battery as do the devices described in U.S. Pat. Nos. 5,335,540 and 5,559,484. U.S. Pat. No. 5,945,908 applies to a stationary tire monitoring system and does not use SAW devices.
One of the first significant SAW sensor patents is U.S. Pat. No. 4,534,223. This patent describes the use of SAW devices for measuring pressure and also a variety of methods for temperature compensation but does not mention wireless transmission.
U.S. Pat. No. 5,987,980 describes a tire valve assembly using a SAW pressure transducer in conjunction with a sealed cavity. This patent does disclose wireless transmission. The assembly includes a power supply and thus this also distinguishes it from a preferred system of this invention. It is a SAW system but as stated in the patent, the antenna for interrogating the device in this design must be within one meter.
U.S. Pat. No. 5,698,786 relates to the sensors and is primarily concerned with the design of electronic circuits in an interrogator. U.S. Pat. No. 5,700,952 also describes circuitry for use in the interrogator to be used with SAW devices. In neither of these patents is the concept of using a SAW device in a wireless tire pressure monitoring system described. These patents also do not describe including an identification code with the temperature and/or pressure measurements in the sensors and devices.
U.S. Pat. No. 5,804,729 describes circuitry for use with an interrogator in order to obtain more precise measurements of the changes in the delay caused by the physical or chemical property being measured by the SAW device. Similar comments apply to U.S. Pat. No. 5,831,167. Other related prior art includes U.S. Pat. No. 4,895,017.
Other patents disclose the placement of an electronic device in the sidewall or opposite the tread of a tire but they do not disclose either an accelerometer or a surface acoustic wave device. In most cases, the disclosed system has a battery and electronic circuits.
One method of measuring pressure that is applicable to this invention is disclosed in V. V. Varadan, Y. R. Roh and V. K. Varadan “Local/Global SAW Sensors for Turbulence”, IEEE 1989 Ultrasonics Symposium p. 591–594 makes use of a polyvinylidene fluoride (PVDF) piezoelectric film to measure pressure. Mention is made in this article that other piezoelectric materials can also be used. Experimental results are given where the height of a column of oil is measured based on the pressure measured by the piezoelectric film used as a SAW device. In particular, the speed of the surface acoustic wave is determined by the pressure exerted by the oil on the SAW device. For the purposes of the instant invention, air pressure can also be measured in a similar manner by first placing a thin layer of a rubber material onto the surface of the SAW device which serves as a coupling agent from the air pressure to the SAW surface. In this manner, the absolute pressure of a tire, for example, can be measured without the need for a diaphragm and reference pressure greatly simplifying the pressure measurement. Other examples of the use of PVDF film as a pressure transducer can be found in U.S. Pat. Nos. 4,577,510 and 5,341,687, which are incorporated by reference herein, although they are not used as SAW devices.
The following U.S. patents provide relevant information to this invention, and to the extent necessary, all of them are incorporated by reference herein: U.S. Pat. Nos. 4,361,026, 4,620,191, 4,703,327, 4,724,443, 4,725,841, 4,734,698, 5,691,698, 5,841,214, 6,060,815, 6,107,910, 6,114,971, 6,144,332.
In recent years, SAW devices have been used as sensors in a broad variety of applications. Compared with sensors utilizing alternative technologies, SAW sensors possess outstanding properties, such as high sensitivity, high resolution, and ease of manufacturing by microelectronic technologies. However, the most attractive feature of SAW sensors is that they can be interrogated wirelessly and that they can be operated without a battery or other source of power except for the RF signal that is captured by the antenna.
1. Signal Boosting
In the use of SAW sensors for vehicles, one problem which arises is that the vibrations of the vehicle can interfere with or create excessive noise in the signals provided by the SAW sensor in view of the generally low strength of the signal from the SAW sensor. In many cases for SAW tire monitors, for example, an adequate return signal can be obtained while the vehicle is stationary but the signal degrades as the vehicle moves. Thus, whereas the device can operate without power in the stationary mode, it is desirable to have a source powered operation for the case when the vehicle is moving. However, when the vehicle is moving there is a significant amount of energy available in the vehicle tire, and elsewhere in the environment, to permit the powered operation of the SAW device. This is known herein as signal boosting. Such signal boosting, as described below, can increase the gain by as much as 6 db in both directions, or a total of 12 db, or more. The energy generated can be stored on a capacitor, or ultracapacitor, or on a rechargeable battery as appropriate.
Previously, RF MEMS switches have not been used in the tire, RFID or SAW sensor environment such as for TPM (tire pressure monitoring) power and antenna switching. International Application No. WO 03/047035A1 entitled “GPS equipped cellular phone using a SPDT MEMS switch and single shared antenna” describes such a use for cell phones. One example of an RF MEMS switch is manufactured by Teravicta Technologies Inc. The company's initial product, the TT612, is a 0 to 6 GHz RF MEMS single-pole, double-throw (SPDT) switch. It has a loss of 0.14-dB at 2-GHz, good linearity and a power handling capability of three watts continuous, all enclosed within a surface mount package.
Teravicta claims the RF performance of its switch is superior to that of conventional solid-state alternatives such as gallium arsenide FETs and PIN diodes that are used in today's wireless voice and data products.
2. Energy Generation
Several of the above referenced patents have disclosed the use of various non-battery power sources for the use with tire monitors. These include inductive, capacitive and generator systems using a moving weight. Other systems that are disclosed herein for the first time to charge an energy storage device use an RFID circuit, the earth's magnetic field with a coil, a solar sensor, a MEMS or other energy generator that uses the vibrations in the tire and a generator that uses the bending deflection of tread or the deflection of the tire itself relative to the tire rim as sources of energy. These can be used with the boosting circuit with or without an RF MEMS or other appropriate mechanical or electronic switch.
3. Communication, ID
The combination of an RFID with a SAW device has also not been reported in the prior art. This combination in addition to providing energy to boost the SAW system can also provide a tire identification to the interrogator. The ID portion of the RFID can be in the form of a SAW Polyvinylidene Fluoride RFID tag that can be manufactured at low cost. The use of such a PVDF SAW RFID has not previously been reported.
4. Miscellaneous enhancements
A SAW pressure sensor can also be used with bladder weight sensors permitting that device to be interrogated wirelessly and without the need to supply power. This also can use the boosting techniques as disclosed herein.
Similarly, a SAW device can be used as a general switch in a vehicle and in particular as a seatbelt buckle switch indicative of seatbelt use.
The operating frequency of SAW devices has previously been limited to less than about 500 MHz due to manufacturing problems. However, recent advances in the manufacture of diamond films that can be combined with a piezoelectric material such as lithium niobate promise to permit higher frequencies to be used.
The SAW-based tire monitor can preferably be mounted in a vertical plane to minimize the effects of centrifugal acceleration.
The use of a SAW-based TPM (tire pressure monitor), and particularly a boosted SAW-based TPM as described herein, permits the after-market replacement for other battery-powered TPM systems such as those manufactured by Schrader with the replacement product removing the need for a battery and thus periodic replacement.
The use of a piezoelectric generator attached to the tire tread also provides a means to measure the tire footprint and thus a measure of the load on the car and truck tires. This can also be accomplished by the system that is powered by the change in distance between the tread and the rim as the tire rotates, coupled with a measure of the pressure within the tire.
In a different but related invention, the driver is provided with a keyless entry device that can be powerless in the form of an RFID or similar device, that can also be boosted as described herein, and the interrogator determines the proximity of the driver to the vehicle door. If the driver remains within 1 meter from the door, for example, for a time period of 5 seconds, for example, then the door automatically unlocks and even opens in some implementations. Thus, as the driver approaches the trunk with his or her arms filled with groceries and pauses, the trunk can automatically open. Such a system would be especially valuable for older people. Naturally, this system can also be used for other systems in addition to vehicle doors and trunk lids.
Objects and Summary of the Invention
It is an object of the present invention to provide new and improved apparatus and methods for boosting signals to signal-receiving and signal-activated sensors, and boosting signals from signal-generating sensors, exemplifying sensors being a SAW device and an RFID tag, or to and/or from a radar, a GPS or other antenna.
It is another object of the present invention to provide a new and improved arrangement including a SAW device and which provides a boost for a signal to and/or from a signal-generating, signal-receiving, or signal-activated sensor such as a SAW device or RFID tag.
It is still another object of the present invention to provide a new and improved two-port circulator for boosting electronic signals, such as signals to and/or from a SAW device or RFID tag.
It is yet another object of the present invention to provide an energy-supply module for supplying energy to an electricity-requiring component derived from movement, such as a sensor on a vehicle whereby energy is provided by motion of the vehicle or a part or component thereof.
Another object of the present invention is to provide a new tire pumping system and tire incorporating the same whereby the rotation of tire causes inflation of the tire.
Yet another object of the present invention is to provide new electricity generating system for tire which generates electricity upon rotation of the tire which can be stored in an storage device, such as a capacitor or rechargeable battery, or used to power a component in the vehicle, such as a tire pump.
In order to achieve at least one of these objects, an arrangement for providing a boosted signal from a signal-generating device such as a SAW device comprises an antenna and a circulator having a first port connected to the antenna to receive a signal from the antenna and a second port adapted to be connected to the SAW device to provide a signal to the SAW device and receive a signal from the SAW device. The circulator amplifies the signal from the antenna such that the amplified signal is directed to the SAW device and amplifies the signal received from the SAW device such that a twice-amplified signal is directed to the antenna. A receiving and processing module is provided to transmit a signal to the antenna causing the antenna to generate its signal and to receive a signal from the antenna derived from the twice-amplified signal.
The circulator may be arranged to provide a signal gain of 6 dB at 400 MHz, for example, so that a round-trip gain of 12 db or more is provided.
The circulator may comprise a first signal splitter arranged in connection with the first port and a second signal splitter arranged in connection with the second port. A first gain mechanism amplifies the signal being directed from the antenna to the SAW device and second gain mechanism amplifies the signal being directed from the SAW device to the antenna.
An energy-supply module may optionally be provided to supply energy to operate the circulator, or another vehicular component. The energy-supply module may comprise a charging capacitor, at least one movable mass, a mechanical-electrical converter coupled to each mass to convert the movement of the mass into electric signals and a bridge rectifier coupled to each converter. The capacitor is coupled to each bridge rectifier to enable charging of the capacitor during movement of the mass(es). Other alternate energy-supply modules may be optionally provided.
The energy-supply module may also comprise an over-charge protector to prevent overcharging of the capacitor, such as a Zener diode arranged in a parallel with the capacitor.
In an embodiment wherein two masses are provided, the masses may be arranged in perpendicular directions.
Several pumping systems for a tire and the like which inflate the tire upon rotation thereof are disclosed. One embodiment includes a housing adapted to be mounted external to the tire and defining a first fluid-receiving chamber. A mass is movable in the housing in response to rotation of the housing and includes a piston rod movable in the first chamber. A first spring is arranged to be compressed by the mass upon movement thereof caused by rotation of the tire. A first inlet valve is arranged in the housing and leads from ambient atmosphere to the first chamber. A first tube is adapted to connect to a nipple or other inlet of the tire. A first exhaust valve is arranged in the housing and provides a flow connection from the first chamber to the first tube. In operation, upon rotation of the tire, the mass moves causing the piston to move in the first chamber and alternately draw air into the first chamber through the first inlet valve and force air through the first exhaust valve into the tube to the nipple to inflate the tire.
To improve the pumping of air into the tire, the housing an also include a second fluid-receiving chamber with the piston rod being movable therein. A second spring is compressed by the mass upon movement thereof in an opposite direction from a direction in which the first spring is compressed by the mass. A second inlet valve is arranged in the housing and leads from ambient atmosphere to the second chamber. A second tube is adapted to connect to a nipple or other inlet of the tire. A second exhaust valve is arranged in the housing and provides a flow connection from the second chamber to the second tube.
With regard to the springs, they may be arranged on opposite sides of the mass and may be linear or non-linear springs.
The housing can include one or more cylinders each defining one or more of the chambers.
An electricity generating system for a vehicle having a tire, which can be used to power a pumping system or charge a battery, comprises a housing adapted to be mounted external to the tire and including a first cylinder defining a first chamber and a first coil wrapped around the first cylinder. A mass is movable in the housing in response to rotation thereof and includes a magnetic piston rod movable in the first chamber. A first spring is compressed by the mass upon movement thereof. An energy storage or load device is connected to the first coil. During vehicular operation, upon rotation of the tire, the mass moves causing the piston to move in the first chamber and impart a charge to the first coil which is stored or used by the energy storage or load device.
The housing may include a second cylinder defining a second chamber and a second coil wrapped around the second cylinder. In this case, the piston rod is movable in the second chamber and the energy storage or load device is connected to the second coil. A second spring is compressed by the mass upon movement thereof in an opposite direction from a direction in which the first spring is compressed by the mass. In operation, upon rotation of the tire, the mass moves causing the piston to alternatingly move in the first and second chambers and impart a charge to the first or second coil which is stored or used by the energy storage or load device. The springs may be arranged on opposite sides of the mass and may be linear or non-linear springs.
Another embodiment of an electricity generating system for a vehicle having a tire in accordance with the invention comprises a housing adapted to be mounted inside the tire and including a coil defining a chamber, a magnetic piston movable in the chamber in response to rotation of the housing and an energy storage or load device connected to the coil. Upon rotation of the tire, the piston moves in the chamber and imparts a charge to the first coil which is stored or used by the energy storage or load device.
Another embodiment of a pumping system for a tire which inflates the tire upon rotation of the tire comprises a housing adapted to be mounted inside the tire and defining an air-receiving chamber, a piston movable in the chamber in response to rotation of the housing and intake mechanism arranged in connection with the piston and adapted to have an inlet external of the tire. The intake mechanism provides a conduit from ambient atmosphere to the chamber. An exhaust valve is arranged in the housing for providing a flow connection from the chamber to an interior of the tire. During vehicular operation, upon rotation of the tire, the piston moves in the chamber and alternately draws air into the chamber through the intake mechanism and forces air through the exhaust valve into the tire. The intake mechanism may comprise a rod for connecting a wheel rim to the piston.
An embodiment of a tire including an electricity generating system in accordance with the invention comprises a rubber substrate defining side walls, a tread, a pad made from a piezoelectric material and attached to an inner surface of the substrate adjacent to the tread and a circuit coupled to the pad and including an energy storage device. During vehicular operation, upon rotation of the tire, the pad flexes causing a charge to appear on opposite sides of the pad thereby creating a voltage which is processed by the circuit to charge the energy storage device. The pad may include a plurality of layers of piezoelectric material, for example, a plurality of sections of piezoelectric material joined together to form a belt stretching around an inner circumference of the substrate. The piezoelectric material may be polyvinylidene fluoride.
Another embodiment of a tire including an electricity generating system comprises a rubber substrate defining side walls, a tread, a housing mounted on an inner surface of the tread and defining an air-receiving chamber and a piston movable in the chamber in response to rotation of the housing. An intake mechanism is arranged in connection with the piston and has an inlet external of the tire when the tire is mounted on a wheel rim. The intake mechanism provides a conduit from the ambient atmosphere, or any location outside of the interior of the tire, to the chamber. An exhaust valve is arranged in the housing and provides a flow connection from the chamber to an interior of the tire. During vehicular operation, upon rotation of the tire, the piston moves in the chamber and alternately draws air into the chamber through the intake mechanism and forces air through the exhaust valve into the tire. The intake mechanism may comprise a rod for connecting a wheel rim to the piston.
Also disclosed herein is a method for providing energy to boost a SAW-based tire pressure monitor which comprises the steps of mounting the SAW-based tire pressure monitor on each tire of a vehicle and coupling a tag to the tire pressure monitor on each tire, each tag including an antenna, a capacitor and an electronic circuit. The electronic circuit includes a circulator having a first port connected to the antenna to receive a signal from the antenna and a second port connected to the tire pressure monitor to provide a signal to the tire pressure monitor and receive a signal from the tire pressure monitor. The circulator receives energy from the capacitor and amplifies the signal from the antenna such that the amplified signal is directed to the tire pressure monitor and also preferably amplifies the signal received from the tire pressure monitor such that a twice-amplified signal is directed to the antenna. The electronic circuit in each tag may include a memory containing a unique identification code for the tag.
Also disclosed is an arrangement for opening a trunk or door of a vehicle including an interrogator adapted to be arranged on the vehicle, a keyless entry device including an antenna and a circuit including a circulator for boosting signals to and from the antenna and a memory containing a unique identification code and a device for opening the trunk or door. The device is coupled to the interrogator and opens the trunk or door when the keyless entry device is a set distance from the interrogator for a certain duration of time.